A side curtain airbag unit has fabric layers forming an inflatable interior with a large surface and a gas generator for filing of the airbag interior. The airbag fabric has an upper edge which is fixed in the area of the roof rail of the motor vehicle, so that the longitudinal direction of the airbag extends along the longitudinal axis of the vehicle. The airbag must be filled with inflation gas from the gas generator from the upper edge. Two concepts are often used in this connection.
In the first concept, the gas generator is located at one of the two ends of the upper edge of the airbag (in most cases at the rear end) and a long, thin metal lance which forms several exit holes extends from the gas generator into the airbag interior and distributes the gas over the length of the airbag.
In a second concept, the airbag exhibits an accommodation area for the gas generator in the area of the upper edge between the front and the rear end. The gas generator extends into the airbag interior or is at least connected with the interior. For this purpose, the accommodation area can be L-shaped, for example.
Generally, cylindrical gas generators are used which are formed so as to be thrust-neutral for reasons of safety. This means that the gas exit openings are arranged rotation symmetrically on an area of the jacket surface of the gas generator. Thus, if an inflator is activated before it is assembled into an airbag system, the inflator will not behave like a rocket which could cause injury and damage. Without additional measures when the inflator is installed in the airbag, this would lead to the problem that the hot gases would stream directly against the airbag fabric and the airbag fabric would possible be damaged during inflation. Therefore deflectors are use, which protect the airbag fabric against the gas when it streams out.
Such a deflector is known from generic patent WO 02/079008 A1, and is in the form of a U-shaped metal sheet. Furthermore, this publication describes a gas guide element of fabric which is sewn into the airbag.
A disadvantage of such a deflector element is that when finally assembled, the airbag unit does not behave in a way which is thrust neutral in the case of a fire. If there should be a fire while the airbag assembly is in storage, the airbag skin consisting of plastic fabric burns, while the gas generator and the deflector element connected with the gas generator remain. In order to fulfill its purpose, namely the purpose of protecting the airbag fabric when the gas is streaming out, however, the deflector element must be construed asymmetrically. From this follows, however, that the subassembly consisting of gas generator and deflector does not behave in a thrust neutral manner. If a fire occurs while the airbag is stored, therefore, an additional hazard is presented by gas generator-deflector subassemblies flying around freely.